Diffusion von Wasserstoff in Metallen

Kehr, K. W.

Book/Report

FZJ-2018-00430

Diffusion von Wasserstoff in Metallen

Kehr, K. W. (Corresponding author)FZJ*

1975
Kernforschungsanlage Jülich, Verlag Jülich

Jülich : Kernforschungsanlage Jülich, Verlag, Berichte der Kernforschungsanlage Jülich 1211, 149 p. (1975)

Please use a persistent id in citations: http://hdl.handle.net/2128/16566

Report No.: Juel-1211

Abstract: Hydrogen in metals bas a large mobility, which at room temperature is several orders or magnitude greater than that or other interstitially dissolved atoms. In this review article the theoretical picture or the diffusion or light interstitials is presented and compared with experiment. In particular possible quantum effects are discussed. First experimental results for the diffusion constants of H, D, and Tin low concentrations in the transition metals, V, Nb, Ta, Ni, and Pd are reviewed. Then the interactions relevant to the remainder of the discussion are introduced, and the problem of the localization of the hydrogen atoms is considered. The classical and quantum-mechanical theories of the single jumps or interstitials are presented. The quantum-mechanical modification or the classical rate thepry is consistent with theresults for the jump rate of the hydrogen atoms above room temperature. The theory yields both an isotope effect in the activation energy and, in the bcc metals, a universal prefactor in the Arrhenius law ror the diffusion constant. On the other hand the completely quantum-mechanical hopping theory cannot quantitativelyexplain the experiment results above room temperature, as is seen by comparing them with calculations or the activation energy and estimates of the isotope effect in the prefactor. Several extensions of theories of the diffusion of light interstitials are examined. The information which can be obtained from quasielastic incoherentneutron scattering is considered in detail. The model or individual jumps between the octahedral sites is appropriate for the fcc metal palladium, but in bcc metals the jump model has not been clearly confirmed. Information about the spatial distribution of a single proton can be obtained from the intensity of the quasielastic line. The intensity to be expected from "tunneling states" in which the protons are distributed quantum-mechanically over several sites is considered. The experimental results at room temperature agree with the picture that the protons essentially perform zero-point oscillations about their equilibrium positions. At higher temperatures anomalies occur in the formtactor of a proton. These anomalies indicate that the picture or fast, unco~related jumps between equilibriwn sites becomes increasingly poorer at higher temperatures. A model which includes a partial delocalization of the proton increasing with increasing temperature is discussed in more detail.

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